Blizzard Criteria Table
| Criterion | Threshold |
|---|---|
| Duration | 3 hours or longer |
| Wind | Sustained or frequent gusts of 35 mph or greater |
| Visibility | Frequently 1/4 mile or less (falling and/or blowing snow) |
| Product | What it means |
|---|---|
| Blizzard Warning | Blizzard conditions expected - the three criteria above, minimum 3 hours |
| Ground Blizzard Warning | Blizzard conditions caused solely by blowing and drifting snow - no new snowfall required |
| Winter Storm Warning | Hazardous winter weather by amount (snow/ice), no wind or visibility bar |
A blizzard is not a big snowfall - it is a visibility event. The NWS glossary definition requires all three of: conditions prevailing for 3 hours or longer, sustained winds or frequent gusts of 35 mph or greater, and considerable falling and/or blowing snow reducing visibility frequently to less than 1/4 mile. Check any forecast against the three tests above; miss one and the storm is merely heavy snow, meet all three and even a 2-inch snowfall blizzards.
Because the bar is wind plus visibility plus time, blowing snow already on the ground can qualify with zero new accumulation - that is exactly what a Ground Blizzard Warning covers, defined as blizzard conditions caused solely by blowing and drifting snow. Great Plains ranch country knows these by heart: clear sky overhead, whiteout at eye level.
How to use
- Enter how many hours the conditions will hold, the wind speed (sustained or frequent gusts), and the visibility in miles.
- The checker lists every criterion your forecast misses, or confirms all three and gives you the word blizzard honestly.
- Use miles for visibility: 0.25 is the 1/4-mile threshold, roughly the length of 2.5 football fields - landmarks vanish well before that.
Frequently asked questions
Does a blizzard require new snowfall?
No. The visibility test is about falling and/or blowing snow, and a ground blizzard - blizzard conditions caused solely by blowing and drifting snow, per the NWS glossary - needs no new accumulation at all. Dry, loose snow left by a previous storm plus 35 mph winds produces full whiteout conditions; this is routine in the Dakotas, Minnesota and the Canadian prairies, and it is why the Ground Blizzard Warning exists as its own product.
What is the difference between a blizzard and a winter storm warning?
A Winter Storm Warning is issued purely on amount - so many inches of snow or a quarter-inch of ice within a window. A Blizzard Warning ignores totals entirely and tests wind, visibility and duration instead. The same storm system can carry both products for different counties: heavy snow without wind on one side of the track, modest snow with 40 mph gusts and whiteout on the other.
Do gusts count, or only sustained winds?
Both count, verbatim: the glossary requires sustained wind or frequent gusts to 35 miles an hour or greater. Gust-driven blizzards are common in mountains and along arctic fronts, where mean wind stays modest but gusts repeatedly hammer visibility to nothing - frequent is the operative word, not occasional.
Is a bomb cyclone the same as a blizzard?
No - they measure different things. Bombogenesis (the bomb cyclone term) describes how fast a low's central pressure falls, roughly 24 millibars in 24 hours; it says nothing about wind, snow or visibility at your location. A bomb cyclone can produce a blizzard, a cold rainstorm, or a sunny windy day - and plenty of classic blizzards, like ground blizzards behind an arctic front, involve no bombogenesis at all.